Search results for "ionic"

1984

The decomposition reactions of the lithiated dimer, trimer, and tetramer of methyl methacrylate (MMA) in THF at 25°C were investigated. The decomposition of the lithiated dimer proceeds via depolymerization to lithiated monomer and MMA, addition of MMA to residual lithiated dimer, resulting the trimer (“disproportionation” of the dimer), and subsequent autocondensation of the products. The lithiated trimer almost exclusively undergoes cyclo-autocondensation, whereas for the lithiated tetramer both reactions proceed simultaneously to a remarkable degree. It is shown that the relative rate of autocondensation, which is highly dependent on the degree of polymerization of the oligomer, controls…

Theoretische analyse der bei einem zweiwegwachstumsmechanismus auftretenden molekulargewichtsverteilungen und ihre anwendung auf die anionische polym…

1967

Es werden mittels der Momentmethode die fur einen abbruchfreien Zweiwegwachstumsmechanismus zu erwartenden Molekulargewichtsverteilungen und ihr Zusammenhang mit dem kinetischen Ablauf theoretisch abgeleitet. Die ermittelten Bezichungen werden auf das Polymerisationssystem Styrol in Cumylmethylather mit Cumylnatrium als Initiator angewandt. Durch Einsetzen der vorher experimentell ermittelten kinetischen Daten in die theoretisch abgeleitete Gleichung werden die Molekulargewichtsverteilungen des untersuchten Systems berechnet und mit den experimentell ermittelten verglichen. Die gute Ubereinstimmung zwischen Theorie und Experiment stellt einen schlussigen Beweis fur das Vorliegen eines Zweiw…

Kinetics of Group Transfer Polymerization

1987

The group transfer polymerization (GTP) of methyl methacrylate (MMA) and tert.-butyl methacrylate (TBMA), catalyzed by bifluoride, is of first order with respect to monomer and catalyst concentrations. A slightly negative order with respect to initiator concentration is observed, indicating an inhibitive function of the initiator. Termination reactions occur at lower catalyst concentrations. They are very pronounced for TBMA and result in incomplete conversions. For MMA, at lower catalyst and higher initiator concentrations, induction periods are observed which increase when lowering the temperature. This is related with the formation of active chains. The Arrhenius plots for the propagatio…

Herstellung, charakterisierung und lösungseigenschaften von einheitlichen styrol-α-methylstyrol block-copolymeren

1977

An improved anionic polymerization technique for the preparation of highly uniform styrene/α-methylstyrene linear two-block copolymers is described. Three sets of samples with molecular weights M were prepared under equal experimental conditions, namely polystyrenes (2 · 105 < M < 3 · 106), poly(α-methylstyrene)s (7 · 104 < M < 4 · 106), and block copolymers (2 · 105 < M < 2,5 · 106). Ultracentrifugation in a density-gradient does not show any chemical heterogeneities in the block copolymers. The molecular polydispersity U = Mw/Mn–1 is U = 0,03 or less as estimated from GPC-measurements. The high molecular and chemical homogeneity of the block copolymers and the optical similarity of the tw…

Some comments on the article of A. A. Korotkov and A. F. Podolsky: On the mechanism of the anionic polymerization of styrene with “living” polystyren…

1966

Polymerisationskinetische und konduktometrische messungen an polystyrylionenpaaren in einem größeren temperaturbereich

1974

Messungen der Bruttogeschwindigkeitskonstante von Polystyryl-Natrium in 3-Methyltetrahydrofuran (3-Me-THF) in Abhangigkeit von der Konzentration der “lebenden” Kettenenden und der Natriumionen ergeben, das die Monomeraddition wie in anderen polaren Losungsmitteln nach einem Mehrwegmechanismus erfolgt. Der Ubergang vom Kontakt- zum solvatgetrennten Ionenpaar wird in einem Temperaturbereich von — 110 bis +85°CC mit Hilfe kinetischer Messungen im Stromungsrohr und durch Leitf ahigkeitsmessungen verfolgt. Analog zu entsprechenden Untersuchungen in Tetrahydrofuran kann dabei die Polymerisation uber jeweils eine Art von Ionenpaaren fast vollstandig isoliert beobachtet werden. Die thermodynamische…

Kinetik der anionischen Polymerisation von Styrol in Dioxan mit Polystyryl-Natrium als Reaktionträger

1971

Die Wachstumskonstante des Polystyryl-Natriums bei der Polymerisation von Styrol in Dioxan wird als Funktion der Konzentration der „lebenden” Enden und der Temperatur gemessen und mit den entsprechenden Werten in anderen Losungsmitteln verglichen. Es zeigt sich, das die Polymerisation in Dioxan ausschlieslich uber das Kontaktionenpaar verlauft. The propagation rate constants of the anionic polymerization of styrene in dioxane were measured as a function of the “living” end concentration and of the temperature. They were compared with corresponding values in other solvents. It is shown that only contact ion-pairs are involved in this polymerization.

Green Solvents for Analytical Separation and Analyses

2010

The alternatives to the use of organic solvents that have been offered by the scientific literature reviewed. In order to look at the best solvents from both analytical and sustainable view points, the use of water under superheated conditions, supercritical fluids, renewable organics, ionic liquids, and aqueous solutions of amphiphillic compounds, have been evaluated. As a general conclusion, it can be seen that, at present, green alternatives to the traditional organic solvents employed in analytical separations and analysis that are being well explored are the capabilities of the use of alcohols, supercritical fluids, and superheated water; and remain unexplored tremendous possibilities …

A Straightforward Route to Homoallyl-Homocrotylamines Promoted by a Titanium Complex

2012

I�-Allyltitanium complexes, generated in situ from 1,3-dienes and Cp2TiH, react with benzotriazole derivatives to give homoallylic amines in good yields. Under similar conditions, triple cascade reactions (allyltitanation followed by cationic 2-aza-Cope rearrangement followed by a second allyltitanation) occur from bis(benzotriazolyl) compounds affording a straightforward route to homoallyl-(E)-homocrotylamines. A theoretical study provides further insight into the factors that govern the selectivity of this sequence of reactions. The titanium-promoted reductive coupling of 1,3-dienes with bis(benzotriazolyl) compounds as substrates led selectively to homoallyl-homocrotylamines through a tr…

1983

Synthese a partir de l'hexahydro-1,5,5a,6,9,9a benzodioxepinne-2,4. Polymerisation en masse en un produit incolore, cireux (Tg=−11°C)